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Abstract:

A variable light transmittance window includes: a substrate configured to
transmit light; a thermochromic layer on the substrate; first function
thin film layers on opposite surfaces of the thermochromic layer; and
second function thin film layers on respective surfaces of the first
function thin film layers opposite the thermochromic layer, wherein a
difference between refractive indices of the first function thin film
layers and the second function thin film layers is greater than a
difference between refractive indices of the first function thin film
layers and the thermochromic layer.

Claims:

1. A variable light transmittance window comprising: a substrate
configured to transmit light; a thermochromic layer on the substrate;
first function thin film layers on opposite surfaces of the thermochromic
layer; and second function thin film layers on respective surfaces of the
first function thin film layers opposite the thermochromic layer, wherein
a difference between refractive indices of the first function thin film
layers and the second function thin film layers is greater than a
difference between refractive indices of the first function thin film
layers and the thermochromic layer.

2. The variable light transmittance window of claim 1, wherein one of the
second function thin film layers, one of the first function thin film
layers, the thermochromic layer, another one of the first function thin
film layers, and another one of the second function thin film layers are
sequentially stacked on the substrate.

5. The variable light transmittance window of claim 1, wherein the
refractive index of the first function thin film layers is greater than
the refractive index of the second function thin film layers.

6. The variable light transmittance window of claim 5, wherein the
difference between the refractive indices of the first function thin film
layers and the second function thin film layers is greater than or equal
to 0.5.

7. The variable light transmittance window of claim 6, wherein the first
function thin film layers have a refractive index that is greater than or
equal to 2.0, and the second function thin film layers have a refractive
index that is less than or equal to 1.5.

8. The variable light transmittance window of claim 7, wherein the
refractive indices decrease from the thermochromic layer to the first
function thin film layers, and from the first function thin film layers
to the second function thin film layers.

10. The variable light transmittance window of claim 9, wherein the first
function thin film layers comprise titanium dioxide (TiO2) and at
least one of vanadium (V) or chromium (Cr).

11. The variable light transmittance window of claim 8, wherein the
second function thin film layers comprise a material selected from the
group consisting of silicon dioxide (SiO2), calcium fluoride
(CaF2), lead fluoride (PbF2), and strontium fluoride
(SrF2).

12. The variable light transmittance window of claim 1, wherein a
thickness of at least one of the first function thin film layers or the
second function thin film layers is approximately 1/4 of a wavelength of
light.

13. The variable light transmittance window of claim 1, wherein reflected
light reflected off of a second surface formed by the layers of the
variable light transmittance window is offset by approximately 1/2 of a
wavelength with respect to reflected light reflected off of a first
surface formed by the layers of the variable light transmittance window.

14. A variable light transmittance window comprising: a substrate
configured to transmit light; a thermochromic layer on the substrate; a
first function thin film layer on the thermochromic layer; and a second
function thin film layer on the first function thin film layer, wherein a
difference between refractive indices of the first function thin film
layer and the second function thin film layer is greater than a
difference between refractive indices of the first function thin film
layer and the thermochromic layer.

16. The variable light transmittance window of claim 14, wherein the
refractive index of the first function thin film layer is greater than
the refractive index of the second function thin film layer.

17. The variable light transmittance window of claim 16, wherein the
difference between the refractive indices of the first function thin film
layer and the second function thin film layer is greater than or equal to
0.5.

18. The variable light transmittance window of claim 17, wherein the
first function thin film layer has a refractive index that is greater
than or equal to 2.0, and the second function thin film layer has a
refractive index that is less than or equal to 1.5.

19. The variable light transmittance window of claim 18, wherein the
refractive indices decrease from the thermochromic layer to the first
function thin film layer, and from the first function thin film layer to
the second function thin film layer.

Description:

RELATED APPLICATIONS

[0001] This application claims the benefit of Korean Patent Application
No. 10-2010-0075668, filed on Aug. 5, 2010, in the Korean Intellectual
Property Office, the disclosure of which is incorporated herein in its
entirety by reference.

BACKGROUND

[0002] 1. Field

[0003] One or more embodiments of the present invention relate to a window
having a light transmittance that varies according to a surrounding
temperature.

[0004] 2. Description of Related Art

[0005] A smart window adjusts transmission of solar light. A material for
adjusting the transmission of solar light is directly applied on the
smart window, and by doing so, it is possible to significantly increase
the transmission of solar light and to provide user convenience, when
compared to a method of attaching a film having a particular fixed
transmission to a window.

[0006] According to types of materials utilized, a smart window may be
classified as a liquid crystal material, a suspended particle display
(SPD), an electrochromic (EC) material, a photochromic (PC) material, or
a thermochromic material, among others.

[0007] From among the aforementioned materials, the transmission of solar
light on a thermochromic smart window varies according to temperature.
Generally, reflectance of a thermochromic smart window is relatively high
at a temperature equal to or greater than a particular (e.g., a
threshold) temperature, and transmission of the thermochromic smart
window is relatively high at a temperature equal to or less than the
particular temperature, with respect to infrared rays having wavelengths
greater than those of visible rays. In the winter when an outdoor
temperature is low, since the transmission of the thermochromic smart
window is higher with respect to infrared rays that emit heat, the
thermochromic smart window transmits the infrared rays so that heating
costs can be saved or reduced. On the other hand, in the summer when the
outdoor temperature is high, since the transmission of the thermochromic
smart window is lower with respect to infrared rays, the thermochromic
smart window blocks the inflow of heat so that cooling costs can be saved
or reduced.

[0008] However, as illustrated in FIG. 1, transmittance with respect to
solar rays in a visible ray range (380-780 nm) of general glass is equal
to or greater than 90%, while, as illustrated in FIG. 2, transmittance
with respect to solar rays in a visible ray range of a glass having a
thermochromic layer formed therein deteriorates by about 30% or more.

SUMMARY

[0009] One or more embodiments of the present invention include a variable
light transmittance window that may increase an energy efficiency in
cooling and heating operations by using a function of a thermochromic
layer, while increasing transmittance in a visible ray range.

[0010] Additional aspects will be set forth in part in the description
which follows and will be apparent from the description, or may be
learned by practice of the presented embodiments.

[0011] According to one or more embodiments of the present invention, a
variable light transmittance window includes a substrate configured to
transmit light; a thermochromic layer on the substrate; first function
thin film layers on opposite surfaces of the thermochromic layer; and
second function thin film layers on respective surfaces of the first
function thin film layers opposite the thermochromic layer, wherein a
difference between refractive indices of the first function thin film
layers and the second function thin film layers is greater than a
difference between refractive indices of the first function thin film
layers and the thermochromic layer.

[0012] One of the second function thin film layers, one of the first
function thin film layers, the thermochromic layer, another one of the
first function thin film layers, and another one of the second function
thin film layers may be sequentially stacked on the substrate.

[0013] The substrate may include glass.

[0014] The thermochromic layer may include vanadium dioxide.

[0015] The refractive index of the first function thin film layers may be
greater than the refractive index of the second function thin film
layers. For example, the difference between the refractive indices of the
first function thin film layers and the second function thin film layers
may be equal to or greater than 0.5. For example, the first function thin
film layers may have a refractive index that is equal to or greater than
2.0, and the second function thin film layers may have a refractive index
that is equal to or less than 1.5.

[0016] The refractive indices may decrease from the thermochromic layer to
the first function thin film layers, and from the first function thin
film layers to the second function thin film layers.

[0018] The first function thin film layers may include titanium dioxide
(TiO2) and at least one of vanadium (V) or chromium (Cr).

[0019] The second function thin film layers may include a material
selected from the group consisting of silicon dioxide (SiO2),
calcium fluoride (CaF2), lead fluoride (PbF2), and strontium
fluoride (SrF2).

[0020] According to one or more embodiments of the present invention, a
variable light transmittance window includes a substrate configured to
transmit light; a thermochromic layer on the substrate; a first function
thin film layer on the thermochromic layer; and a second function thin
film layer on the first function thin film layer, wherein a difference
between refractive indices of the first function thin film layer and the
second function thin film layer is greater than a difference between
refractive indices of the first function thin film layer and the
thermochromic layer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] These and/or other aspects will become apparent and more readily
appreciated from the following description of the embodiments, taken in
conjunction with the accompanying drawings, of which:

[0022] FIG. 1 is a graph illustrating light transmittance with respect to
wavelengths in general glass;

[0023]FIG. 2 is a graph illustrating light transmittance with respect to
wavelengths in glass having a thermochromic layer formed therein;

[0024]FIG. 3 is a cross-sectional view of a variable light transmittance
window according to an embodiment of the present invention;

[0025]FIG. 4 is a graph illustrating light transmittance with respect to
wavelengths in the variable light transmittance window of FIG. 3;

[0026] FIG. 5 is a cross-sectional view of a variable light transmittance
window according to another embodiment of the present invention;

[0027] FIG. 6 is a graph illustrating light transmittance with respect to
wavelengths in the variable light transmittance window of FIG. 5;

[0028]FIG. 7 is a cross-sectional view of a variable light transmittance
window according to a comparative example; and

[0029] FIG. 8 is a graph illustrating light transmittance with respect to
wavelengths in the variable light transmittance window of FIG. 7.

DETAILED DESCRIPTION

[0030] Reference will now be made in detail to embodiments, examples of
which are illustrated in the accompanying drawings, wherein like
reference numerals refer to like elements throughout. In this regard, the
present embodiments may have various different forms and should not be
construed as being limited to the descriptions set forth herein.
Accordingly, the embodiments are merely described below, in reference to
the figures, to explain various aspects of the present invention.

[0031]FIG. 3 is a cross-sectional view of a variable light transmittance
window according to an embodiment of the present invention. FIG. 4 is a
graph illustrating light transmittance with respect to wavelengths in the
variable light transmittance window of FIG. 3.

[0032] The variable light transmittance window according to the present
embodiment is formed of a glass 11, which may serve as a substrate, and a
variable light transmittance layer formed on the glass 11. The variable
light transmittance layer includes a thermochromic layer 15, a first
function thin film layer 13 formed on both surfaces of the thermochromic
layer 15, and a second function thin film layer 12 formed on both
surfaces of the first function thin film layer 13. That is, the glass 11,
the second function thin film layer 12 having a low dielectric constant,
the first function thin film layer 13 having a high dielectric constant,
the thermochromic layer 15, the first function thin film layer 13 having
the high dielectric constant, and the second function thin film layer 12
having the low dielectric constant may be sequentially stacked from the
bottom up.

[0033] The thermochromic layer 15 may be formed of a vanadium
dioxide-based material.

[0034] The first function thin film layer 13 may be formed of a high
dielectric material having a high refractive index equal to or greater
than 2.0. For example, the first function thin film layer 13 may include
titanium dioxide (TiO2), bismuth oxide (Bi2O3), chromium
oxide (Cr2O3), gadolinium oxide (Gd2O3), germanium
(Ge), indium tin oxide (ITO), lead telluride (PbTe), tantalum oxide
(Ta2O5), and the like.

[0035] The second function thin film layer 12 may be formed of a low
dielectric material having a low refractive index equal to or less than
1.5. For example, the second function thin film layer 12 may include
silicon dioxide (SiO2), calcium fluoride (CaF2), lead fluoride
(PbF2), strontium fluoride (SrF2), and the like.

[0036] Refractive indices of the present embodiment are shown in Table 1,
wherein the present embodiment corresponds to a case in which the first
function thin film layer 13 is formed of TiO2 and the second
function thin film layer 12 is formed of SiO2,

[0037] As shown above, the first function thin film layers 13, having a
refractive index similar to that of the thermochromic layer 15, are
arranged as layers neighboring with or adjacent to the thermochromic
layer 15. A refractive index difference between the thermochromic layer
15 and its neighboring layers may be small (e.g., as small as possible).
By doing so, reflectance at an interface of the thermochromic layer 15 is
decreased, so that transmittance in a visible ray range of the variable
light transmittance window may be increased.

[0038] The TiO2 layer serving as the first function thin film layer
13 in the present embodiment is adjacent to the thermochromic layer 15,
prevents oxidation of the thermochromic layer 15, and has a self-cleaning
characteristic, thereby enhancing durability of a multi-thin film layer.

[0039] Also, the second function thin film layers 12, having a refractive
index that is different from the refractive index of the first function
thin film layers 13 are arranged as layers neighboring with or adjacent
to the first function thin film layers 13, for example, on a side of the
first function thin film layers 13 opposite the thermochromic layer 15.
The difference between the refractive indices of the first and second
function thin film layers 13 and 12 may be large (e.g., as large as
possible). When refractive indices of thin film layers are n1 and n2,
respectively, reflectance is obtained by using Equation [(n1-n2)/(n1+n2)]
2. Thus, as the difference between the refractive indices of the thin
film layers increases, the reflectance increases. By doing so, reflection
occurs at interfaces between the first function thin film layers 13
having the high dielectric constant and the second function thin film
layers 12 having the low dielectric constant, and lights reflected from
the interfaces overlap with each other to affect interference.

[0040] The SiO2 layer serving as the second function thin film layer
12 in the present embodiment is adjacent to the TiO2 layer, so that
durability of the SiO2 layer is enhanced.

[0041] Here, a thickness of each layer of the first and second function
thin film layers may be 1/4 of a wavelength λ of light. In the case
of two reflective surfaces having different refractive indices, lights
reflected from the two reflective surfaces interfere with each other to
determine a final reflectance. In this regard, when a thickness of a
layer corresponding to a distance between the two reflective surfaces is
(1/4)λ, light reflected from the second reflective surface is
delayed or offset by (1/2)λ with respect to light reflected from
the first reflective surface, so that destructive interference occurs
between the two reflected lights due to a 180 degree phase difference. As
such, reflectance is decreased, and transmittance is increased. More
specifically, when the first reflective surface and the second reflective
surface exist, if reflection occurs at the first reflective surface and
the second reflective surface at a same phase shift or difference,
reflectance is increased due to constructive interference, but if
reflection occurs at the first reflective surface and the second
reflective surface at an opposite phase shift or difference, reflectance
is decreased due to destructive interference. By having a sufficient or
appropriate distance between the two reflective surfaces to cause
destructive interference, the two reflective surfaces may have or form an
anti-reflection characteristic or property.

[0042] In addition to TiO2, a small amount of vanadium (V), chromium
(Cr), and the like may be added to the first function thin film layers
13. Since TiO2 has a high bandgap of 3.2 eV, if a small amount of
vanadium (V), chromium (Cr), and/or the like are added to TiO2, so
as to function as a visible ray responsive-type catalyst, a band
absorbing portion is moved, so that activity of the visible ray range may
be increased.

[0043] Referring to FIG. 4, it is evident that the variable light
transmittance window having a configuration shown in FIG. 3 has achieved
about a 30% increase in the transmittance of the visible ray range,
compared to a configuration only having the thermochromic layer 15.

[0044] FIG. 5 is a cross-sectional view of a variable light transmittance
window according to another embodiment of the present invention. FIG. 6
is a graph illustrating light transmittance with respect to wavelengths
in the variable light transmittance window of FIG. 5.

[0045] The variable light transmittance window according to the present
embodiment is formed of a glass 21, which may serve as a substrate, and a
variable light transmittance layer formed on the glass 21. The variable
light transmittance layer includes a thermochromic layer 25, a first
function thin film layer 23 formed on a surface of the thermochromic
layer 25, and a second function thin film layer 22 formed on a surface of
the first function thin film layer 23. That is, the glass 21, the
thermochromic layer 25, the first function thin film layer 23 having a
high dielectric constant, and the second function thin film layer 22
having a low dielectric constant may be sequentially stacked from the
bottom up.

[0046] In the present embodiment, the first function thin film layer 23
and the second function thin film layer 22 may be the same as or similar
to those of FIG. 3, and thus descriptions thereof are not provided here.

[0047] Refractive indices of the present embodiment are shown in Table 2,
wherein the present embodiment corresponds to a case in which the first
function thin film layer 23 is formed of TiO2 and the second
function thin film layer 22 is formed of SiO2.

[0048] As shown above, the first function thin film layer 23, having a
refractive index similar to that of the thermochromic layer 25, is
arranged as a layer neighboring with or adjacent to the thermochromic
layer 25. A refractive index difference between the thermochromic layer
25 and the first function thin film layer 23 may be small (e.g., as small
as possible). By doing so, reflectance at an interface of the
thermochromic layer 25 is decreased, so that transmittance in a visible
ray range of the variable light transmittance window is increased.

[0049] Also, the second function thin film layer 22 having a refractive
index that is different from the refractive index of the first function
thin film layer 23 is arranged as a layer neighboring with or adjacent to
the first function thin film layer 23 on a side of the first function
thin film layer 23 opposite the thermochromic layer 25. The difference
between the refractive indices of the first and second function thin film
layers 23 and 22 may be large (e.g., as large as possible). By doing so,
reflection occurs at an interface between the first function thin film
layer 23 having the high dielectric constant and the second function thin
film layer 22 having the low dielectric constant, and lights reflected
from the reflective surfaces overlap with or interfere with each other to
affect interference.

[0050] The SiO2 layer serving as the second function thin film layer
22 in the present embodiment is adjacent to the TiO2 layer, so that
durability of the SiO2 layer is enhanced.

[0051] Referring to FIG. 6, it is evident that the variable light
transmittance window having a configuration shown in FIG. 5 has achieved
about a 20% increase in the transmittance of the visible ray range,
compared to a configuration only having the thermochromic layer 25.

[0052]FIG. 7 is a cross-sectional view of a variable light transmittance
window according to a comparative example. FIG. 8 is a graph illustrating
light transmittance with respect to wavelengths in the variable light
transmittance window of FIG. 7.

[0053] In the variable light transmittance window according to the
comparative example, a glass 31, a first function thin film layer 33
having a high dielectric constant, a second function thin film layer 32
having a low dielectric constant, a thermochromic layer 35, a second
function thin film layer 32 having a low dielectric constant, and a first
function thin film layer 33 having a high dielectric constant are
sequentially stacked from the bottom up. That is, compared to the
aforementioned embodiments, the comparative example is different in that
the second function thin film layers 32 having a low dielectric constant
are arranged as layers neighboring with or adjacent to the thermochromic
layer 35.

[0054] Referring to FIG. 8, it is evident that a transmittance of a
visible ray range in the variable light transmittance window having a
configuration shown in FIG. 7 has further decreased, compared to the
variable light transmittance window only having the thermochromic layer
35. This is because the thermochromic layer 35 is added and then the
first and second function thin film layers 33 and 32 are further added in
the above arrangement, such that transparency of the variable light
transmittance window deteriorates.

[0055] Smart windows formed by applying variable light transmittance
windows according to the first and second embodiments respectively
include the thermochromic layers 15 and 25 in which transmittance is
gradually changed around a threshold temperature. That is, the smart
windows have a characteristic that the transmittance of the smart windows
are relatively low at a temperature equal to or greater than a particular
temperature, and the transmittance of the smart windows is relatively
high at a temperature equal to or less than the particular temperature,
with respect to infrared rays having wavelengths greater than those of
visible rays. By doing so, in the winter when an outdoor temperature is
low, since the transmittance of the smart windows is higher with respect
to infrared rays emitting heat, the smart windows transmit the infrared
rays so that heating costs can be saved. On the other hand, in the summer
when the outdoor temperature is high, since the transmittance of the
smart windows is lower with respect to infrared rays, the smart windows
block the inflow of heat so that cooling costs can be saved.

[0056] In particular, in order to prevent or reduce a decrease in
transmittance due to the forming of the thermochromic layers 15 or 25,
the first function thin film layers 13 and 23 having a high dielectric
constant are formed as layers respectively neighboring with or adjacent
to the thermochromic layers 15 and 25 having a high dielectric constant,
and the second function thin film layers 12 and 22 having a low
dielectric constant are formed on the first function thin film layers 13
and 23, respectively, so as to form a large refractive index difference,
so that the decrease of the transmittance may be minimal or reduced. By
doing so, oxidation of the thermochromic layers 15 and 25 is also
prevented or reduced, so that the durability of the multi-thin film layer
may also be enhanced.

[0057] The variable light transmittance windows according to embodiments
of the present invention are configured in a manner that an energy
efficiency in cooling and heating operations is increased due to the
thermochromic layer, while additional functional layers are appropriately
arranged, such that the transmittance of the visible ray range may be
increased. In addition, due to the function layers formed on the
thermochromic layer, the durability of the thermochromic layer may also
be enhanced.

[0058] Embodiments of the present invention may be used in various
industrial fields, including but not limited to smart windows.

[0059] It should be understood that the exemplary embodiments described
herein should be considered in a descriptive sense only, and not for
purposes of limitation. Descriptions of features or aspects within each
embodiment should be considered as available for other similar features
or aspects in other embodiments. It should also be understood that the
invention is intended to cover various modifications and equivalent
arrangements included within the spirit and scope of the appended claims,
and equivalents thereof.